Interdigitated cellular cushioning

CROSS-REFERENCE TO RELATED APPLICATIONS

0001The present application is a continuation of U.S. patent application Ser. No. 13/323,611 filed Dec. 12, 2011, (now allowed) which claims benefit of priority to U.S. Provisional Patent Application No. 61/421,713, entitled “Interdigitated Cellular Cushioning” and filed on Dec. 10, 2010, which are specifically incorporated by reference herein for all that they disclose or teach. The present application is further related to International Patent Application No. PCT/US11/64449, published as WO 2012/079082 and entitled “Interdigitated Cellular Cushioning,” and filed under the Patent Cooperation Treaty on Dec. 12, 2011, which is also specifically incorporated by reference herein for all that it discloses or teaches.

BACKGROUND

0002Cushioning systems are used in a wide variety of applications including comfort and impact protection of the human body. A cushioning system is placed adjacent a portion of the body (with one or more layers of material between the body and the cushioning system, in some implementations) and provides a barrier between the body and one or more objects impinging on the body. For example, a foam floor mat contains multiple voids filled with air that cushion the body from a hard floor surface. Similarly, chairs, gloves, knee-pads, helmets, etc. may include a cushioning system that provides a barrier between a portion of the body and one or more objects impinging on that portion of the body.

0003A variety of structures are used for cushioning systems. For example, an array of closed-cell air chambers often constitutes various impact protection padding (e.g., pads and helmets). Further examples include open or closed cell foam and elastomeric honeycomb structures. These structures may break down over time and often lack a controlled spring rate or rates over the entire deformation range of the structures.

SUMMARY

0004Implementations described and claimed herein address the foregoing problems by providing an interdigitated cellular cushioning system comprising a first sheet of resilient material including a first binding layer and a first array of void cells protruding from the first binding layer; and a second sheet of resilient material including a second binding layer and a second array of void cells protruding from the second binding layer, wherein the void cells are configured to monotonically collapse under a load, wherein a peak of each void cell in the first array contacts the second binding layer and a peak of each void cell in the second array contacts the first binding layer, and wherein at least one void cell in the first array is attached to the second binding layer and at least one void cell in the second array is attached to the first binding layer.

0005Further implementations described and claimed herein address the foregoing problems by providing a method of absorbing kinetic energy comprising monotonically collapsing a first sheet of resilient material including a first binding layer and a first array of void cells protruding from the first binding layer and monotonically collapsing a second array of void cells protruding from a second binding layer of a second sheet of resilient material without collapsing the second binding layer, wherein a peak of each void cell in the first array contacts the second binding layer and a peak of each void cell in the second array contacts the first binding layer, and wherein at least one void cell in the first array is attached to the second binding layer and at least one void cell in the second array is attached to the first binding layer.

0006Still further implementations described and claimed herein address the foregoing problems by providing a method of manufacturing an interdigitated cellular cushioning system comprising molding a first sheet of resilient material into a first binding layer with a first array of void cells protruding from the first binding layer; molding a second sheet of resilient material into a second binding layer with a second array of void cells protruding from the second binding layer; molding a third sheet of resilient material into a third binding layer with a third array of void cells protruding from the third binding layer; molding a fourth sheet of resilient material into a fourth binding layer with a fourth array of void cells protruding from the fourth binding layer; and welding a peak of a void cell in the first array to the second binding layer, the third binding layer, and a peak of a void cell in the fourth array.

0007Other implementations are also described and recited herein.

BRIEF DESCRIPTIONS OF THE DRAWINGS

<figref idref="DRAWINGS">FIG. 1</figref> illustrates two users standing on a surface incorporating an example interdigitated cellular cushioning system.

<figref idref="DRAWINGS">FIG. 2</figref> illustrates a perspective view of an example interdigitated cellular cushioning system.

<figref idref="DRAWINGS">FIG. 3</figref> illustrates an elevation view of an example interdigitated cellular cushioning system.

<figref idref="DRAWINGS">FIG. 4</figref> illustrates an elevation view of an example 2-layer interdigitated cellular cushioning system.

<figref idref="DRAWINGS">FIG. 5</figref> illustrates a plan view of an example interdigitated cellular cushioning system.

<figref idref="DRAWINGS">FIG. 6</figref> illustrates an elevation view of an example interdigitated cellular cushioning system in an unloaded state.

<figref idref="DRAWINGS">FIG. 7</figref> illustrates an elevation view of an example interdigitated cellular cushioning system loaded in a first load range.

<figref idref="DRAWINGS">FIG. 8</figref> illustrates an elevation view of an example interdigitated cellular cushioning system loaded in a second load range.

<figref idref="DRAWINGS">FIG. 9</figref> illustrates an elevation view of an example interdigitated cellular cushioning system loaded in a third load range.

<figref idref="DRAWINGS">FIG. 10</figref> illustrates an elevation view of an example interdigitated cellular cushioning system loaded in a fourth load range.

<figref idref="DRAWINGS">FIG. 11</figref> illustrates an example force over displacement graph with four load ranges, each with unique spring rate characteristics.

<figref idref="DRAWINGS">FIG. 12</figref> illustrates a first example force over time graph comparing impact performance of an interdigitated cellular cushioning system with impact performance of opposed void cellular cushioning systems.

<figref idref="DRAWINGS">FIG. 13</figref> illustrates a second example force over time graph comparing impact performance of two interdigitated cellular cushioning systems with impact performance of an opposed void cellular cushioning system.

<figref idref="DRAWINGS">FIG. 14</figref> illustrates a third example force over time graph comparing impact performance of an interdigitated cellular cushioning system with impact performance of an opposed void cellular cushioning system.

<figref idref="DRAWINGS">FIG. 15A</figref> illustrates an example uncompressed cell in an interdigitated cellular cushioning system.

<figref idref="DRAWINGS">FIG. 15B</figref> illustrates an example cell in an interdigitated cellular cushioning system compressed in a first load range.

<figref idref="DRAWINGS">FIG. 15C</figref> illustrates an example cell in an interdigitated cellular cushioning system compressed in a second load range.

<figref idref="DRAWINGS">FIG. 15D</figref> illustrates an example cell in an interdigitated cellular cushioning system compressed in a third load range.

<figref idref="DRAWINGS">FIG. 15E</figref> illustrates an example cell in an interdigitated cellular cushioning system compressed in a fourth load range.

<figref idref="DRAWINGS">FIG. 16</figref> illustrates example operations for using an interdigitated cellular cushioning system.

<figref idref="DRAWINGS">FIG. 17</figref> illustrates an example thermoforming manufacturing process for making a 2-layer interdigitated cellular cushioning system.

<figref idref="DRAWINGS">FIG. 18</figref> illustrates example operations for manufacturing an interdigitated cellular cushioning system.

DETAILED DESCRIPTIONS

0030<figref idref="DRAWINGS">FIG. 1</figref> illustrates two users <b>102</b>, <b>104</b> standing on a floor <b>106</b> incorporating an example interdigitated cellular cushioning system <b>108</b>. The floor <b>106</b> is the traction or standing surface of a vehicle, building, or other structure, for example. Attached to a bottom surface of the floor <b>106</b> is the cushioning system <b>108</b>. In some implementations, a top binding layer <b>112</b> of the cushioning system <b>108</b> may serve as the floor <b>106</b>. In other implementations, the cushioning system <b>108</b> is utilized under the floor <b>106</b>. Below the cushioning system <b>108</b> is a protective or load distributing layer <b>120</b> that is attached to a bottom binding layer <b>114</b> of the cushioning system <b>108</b>. In one implementation, the protective layer <b>120</b> is armor to protect the users <b>102</b>, <b>104</b> from incoming projectiles. In other implementation, the protective layer <b>120</b> is merely another layer of the floor. In some implementations, the protective layer <b>120</b> is not included.

0031The cushioning system <b>108</b> includes void cells (e.g., void cells <b>110</b>, <b>116</b>) or support units arranged in a matrix bounded by the top binding layer <b>112</b> and the bottom binding layer <b>114</b>. The cells alternate facing upwards and downward. In one implementation, each upward facing cell (e.g., cell <b>116</b>) is surrounded by downward facing cells and each downward facing cell (e.g., cell <b>110</b>) is surrounded by upward facing cells. The void cells are hollow chambers that resist deflection due to compressive forces, similar to compression springs. In one implementation, each upward facing cell is a protrusion of the top binding layer <b>112</b> and each downward facing cell is a protrusion of the bottom binding layer <b>114</b>. Each peak (e.g., peak <b>118</b>) of the upward facing cells is attached to the bottom binding layer <b>114</b>. Similarly, each peak of the downward facing cells is attached to the top binding layer <b>112</b>. The binding layers <b>112</b>, <b>114</b> link the void cells together forming the interdigitated cellular cushioning system <b>108</b>.

0032In the event of an explosion (e.g., explosion <b>122</b>), or other large impulse of kinetic energy (e.g., a physical impact), the protective layer <b>120</b> may buckle as shown or may also be punctured or ruptured. Upward deflection of the protective layer <b>120</b> is absorbed by the cushioning system <b>108</b>. Cells adjacent the explosion <b>122</b> are compressed in various states to ensure that minimal energy is transmitted through the floor <b>106</b> to the users <b>102</b>, <b>104</b>. In some implementations with particularly large explosions or impacts, the floor <b>106</b> may be affected some, but to a lesser extent than the protective layer <b>120</b>. The end result is that much of the upward movement of the protective layer and the energy created by the explosion <b>122</b> are largely absorbed by the cushioning system <b>108</b> and injury to the users <b>102</b>, <b>104</b> is reduced or prevented because the floor <b>106</b> is relatively unaffected.

0033In a further application, the cushioning system <b>108</b> may be used to change a path of an incoming projectile. Changing the path of a pointed projectile, such as a bullet, can reduce the projectile's effectiveness at penetrating a surface. For example, if a bullet penetrates the protective layer <b>120</b> and proceeds into the cushioning system <b>108</b>, the cushioning system <b>108</b> may not significantly reduce the kinetic energy of the bullet as the bullet passes through the cushioning system <b>108</b>. However, the varying structures (e.g., the void cells) in the cushioning system <b>108</b> may cause the bullet to turn or start to tumble. As a result, the bullet's effectiveness at penetrating the floor <b>106</b> is reduced and the users <b>102</b>, <b>104</b> are better protected.

0034<figref idref="DRAWINGS">FIG. 2</figref> illustrates a perspective view of an example interdigitated cellular cushioning system <b>208</b>. The cushioning system <b>208</b> includes void cells (e.g., void cell <b>210</b>) arranged in a matrix bounded by the top binding layer <b>212</b> and a bottom binding layer <b>214</b>. The cells alternate facing upwards and downward. In one implementation, each upward facing cell inward from the edges of the cushioning system <b>208</b> panel (e.g., cell <b>216</b>) is surrounded on all four sides by downward facing cells and each downward facing cell inward from the edges of the cushioning system <b>208</b> panel are similarly surrounded on all four sides by upward facing cells. Void cells on the edge of the system panel (e.g., cell <b>210</b>) are surrounded by upward facing cells on less than four sides (e.g., cell <b>210</b> is surrounded on three sides). Interdigitation of the void cells may aid the cushioning system <b>208</b> in resisting non-normal loads, at least when compared to other materials incorporating energy-absorbing geometry. More specifically, shear forces along the top and bottom binding layers <b>212</b>, <b>214</b> may not significantly impact the energy absorbing capability of the cushioning system <b>208</b> due at least in part to the interdigitation of the void cells.

0035The void cells are hollow chambers that resist deflection due to compressive forces, similar to compression springs. The force-deflection profile or spring rate profile (i.e., compressive force required per unit of compressive displacement) of the matrix of void cells is configurable based on the intended application of the cushioning system <b>208</b>. Further, the spring rates of the void cells in combination with overall cushioning system <b>212</b> thickness can provide a desired energy absorption for an expected range of kinetic energies that may be applied to the cushioning system <b>212</b>.

0036At least a choice of material, wall thickness, size, spacing, and shape of each of the void cells defines the resistive force each of the void cells can apply. Materials used for the void cells are generally elastically deformable under expected load conditions and will withstand numerous deformations without fracturing. Example materials include engineering grade plastic elastomers (e.g., thermoplastic urethane, Dow Pellethane®, and Lubrizol Estane®), styrene copolymers, metallocenes, thermoplastic polyester elastomers (e.g., Dupont™ Hytrel®), ethylene-vinyl acetate, thermoplastic vulcanisate, and rubber. Further, the wall thickness of each of the void cells may range from 0.005 to 0.1 inches. In some implementations, the wall thickness of each void cell varies over a height of the void cell (e.g., the void cells may each be thinner at the base and thicker at the peak). This phenomenon may be a by-product of the manufacturing process or may be intentionally designed into the manufacturing process. Still further, the size of each of the void cells may range from 0.2 to 3 inches in diameter and height.

0037Further yet, the void cells may be cubical, pyramidal, hemispherical, hemiellipsoidal, conical, truncated conical, or any other shape capable of having a hollow interior volume. Still further, the void cells may be characterized as columns or tapered columns. Still further, the void cells may be spaced a variety of distances from one another. For example, a more tightly spaced matrix of void cells will likely result in a greater energy absorption value than a more loosely spaced matrix of void cells. An example spacing range is nearly zero (or touching) to 3 inches or more between void cells. Further, the aforementioned features of the void cells may not be uniform throughout the cushioning system <b>208</b>. For example, features of each of the void cells attached to the top binding layer may vary from features of each of the void cells attached to the bottom binding layer. The features of the void cells, whether they are uniform across the cushioning system or not, are designed to yield a desired spring rate profile (see e.g., <figref idref="DRAWINGS">FIG. 11</figref>). The aforementioned dimensions are examples only; the cushioning system <b>208</b> may utilize dimensions outside of the given ranges.

0038In one implementation, each upward facing cell is a protrusion of the top binding layer <b>212</b> and each downward facing cell is a protrusion of the bottom binding layer <b>214</b>. Each peak of the upward facing cells is attached to the bottom binding layer <b>214</b>. Similarly, each peak (e.g., peak <b>218</b>) of the downward facing cells is attached to the top binding layer <b>212</b>. The binding layers <b>212</b>, <b>214</b> link the void cells together forming the interdigitated cellular cushioning system <b>208</b>. In other implementations, the upward and downward facing cells are not protrusions of the top and bottom binding layers <b>212</b>, <b>214</b>. Instead, the upward and downward facing cells are merely attached to the top and bottom binding layers <b>212</b>, <b>214</b>. The top and bottom binding layers <b>212</b>, <b>214</b> may be constructed with the same potential materials as the void cells and in one implementation are contiguous with each of the void cells. One or more coupling ribs (not shown) may be attached to the exterior of the void cells extending vertically to the top and/or bottom binding layers <b>212</b>, <b>214</b>. These ribs can add additional stiffness to the void cells.

0039The void cells are filled with ambient air, a foam, or a fluid other than air, for example. The foam or certain fluids may be used to add insulation or additional resistance to deformation to the cushioning system <b>208</b>. In a vacuum environment, the void cells may be un-filled. By not relying on air pressure for resistance to deflection, the void cells can achieve a controlled spring rate that is not necessarily linear (e.g., as with a traditional coil spring), or exponentially increasing (e.g., as with a closed chamber of air with non-elastic walls). Air and/or water could be forced through voids between the upward and downward facing cells to facilitate cleaning substantially all of the surfaces of the components of the cushioning system <b>208</b>. Further, these surfaces of the cushioning system <b>208</b> could be treated with an anti-microbial substance or the cushioning system <b>208</b> material itself could be anti-microbial.

0040The cushioning system <b>208</b> may be manufactured using a variety of manufacturing processes (e.g., blow molding, forming extrusion, injection molding, reaction injection molding (RIM), vacuum forming, laminating, etc.). In one implementation, the cushioning system <b>208</b> is manufactured in two halves. A first half comprises the top binding layer <b>212</b> with void cells protruding therefrom. A second half comprises the bottom binding layer <b>214</b>, also with void cells protruding therefrom. The two halves are then placed adjacent one another with void cells from the top binding layer <b>212</b> protruding toward the bottom binding layer <b>214</b> and vice versa. The void cells from the top binding layer <b>212</b> alternate with the void cells from the bottom binding layer <b>214</b>. Peaks or tops (e.g., peak <b>218</b>) of each of the void cells in the top binding layer <b>212</b> are then laminated or glued to the bottom binding layer <b>214</b>, and vice versa. In one implementation, the top binding layer <b>212</b> and the bottom binding layer <b>214</b> are not required to be precisely aligned because the interdigitated void cells naturally find a position between one another when positioned together for the welding or gluing process. As a result, manufacturing costs may be reduced. Further, multiple weld points between the top binding layer <b>212</b> and the bottom binding layer <b>214</b> makes a very strong bond between the layers <b>212</b>, <b>214</b>. In another implementation, the cushioning system <b>208</b> is manufactured in one piece rather than two pieces as discussed above. Further, a cushioning system according to the presently disclosed technology may include two or more matrices of interdigitated void cells (i.e., two or more cushioning systems <b>208</b>) stacked on top of one another.

0041<figref idref="DRAWINGS">FIG. 3</figref> illustrates an elevation view of an example interdigitated cellular cushioning system <b>308</b>. The cushioning system <b>308</b> includes void cells (e.g., void cell <b>310</b>) arranged in a matrix bounded by a top binding layer <b>312</b> and a bottom binding layer <b>314</b>. The cells alternate facing upwards and downward. In one implementation, each upward facing cell (e.g., cell <b>316</b>) is surrounded by downward facing cells and each downward facing cell (e.g., cell <b>310</b>) is surrounded by upward facing cells. The void cells are hollow chambers that resist deflection due to compressive forces, similar to compression springs. The force-deflection profile of the matrix of void cells is configurable based on the intended application of the cushioning system <b>308</b>.

0042Each upward facing cell is a protrusion of the top binding layer <b>312</b> and each downward facing cell is a protrusion of the bottom binding layer <b>314</b>. Each peak (e.g., peak <b>318</b>) of the upward facing cells is attached to the bottom binding layer <b>314</b>. Similarly, each peak of the downward facing cells is attached to the top binding layer <b>312</b>. The binding layers <b>312</b>, <b>314</b> link the void cells together forming the interdigitated cellular cushioning system <b>308</b>. In other implementations, the upward and downward facing cells are not protrusions of the top and bottom binding layers <b>312</b>, <b>314</b>. Instead, the upward and downward facing cells are merely attached to the top and bottom binding layers <b>312</b>, <b>314</b>. One or more coupling ribs <b>324</b> may be attached to the exterior of the void cells extending vertically to the top and/or bottom binding layers <b>312</b>, <b>314</b>. These ribs can add additional stiffness to the void cells.

0043<figref idref="DRAWINGS">FIG. 4</figref> illustrates an elevation view of an example 2-layer interdigitated cellular cushioning system <b>408</b>. The cushioning system <b>408</b> includes two layers <b>411</b>, <b>415</b> of void cells (e.g., void cell <b>416</b>). Each layer <b>411</b>, <b>415</b> is arranged in a matrix bounded by two binding layers. The top layer <b>411</b> is arranged in a matrix bounded by a top binding layer <b>412</b> and a middle binding layer <b>413</b>. The bottom layer <b>415</b> is arranged in a matrix bounded by the middle binding layer <b>413</b> and a bottom binding layer <b>414</b>.

0044The cells in each layer <b>411</b>, <b>415</b> alternate facing upwards and downward. In one implementation, each upward facing cell (e.g., cell <b>416</b>), excepting cells on the edge or corner of the cushioning system <b>408</b>, is surrounded on four sides by downward facing cells and each downward facing cell (e.g., cell <b>410</b>), excepting cells on the edge or corner of the cushioning system <b>408</b>, is surrounded on four sides by upward facing cells. Further each peak (e.g., peak <b>418</b>) of the top layer <b>411</b> may be aligned with each peak of the bottom layer <b>415</b>. Similarly, each hollow chamber of each void cell in the top layer <b>411</b> may be aligned with each hollow chamber of each void cell in the bottom layer <b>415</b>. The void cells are hollow chambers that resist deflection due to compressive forces, similar to compression springs. The force-deflection profile of the matrix of void cells is configurable based on the intended application of the cushioning system <b>408</b>.

0045The upward facing cells are protrusions of the middle binding layer <b>413</b> or the top binding layer <b>412</b>. Similarly, the downward facing cells are protrusions of the middle binding layer <b>413</b> or the bottom binding layer <b>414</b>. The peaks of the upward facing cells are attached to the middle binding layer <b>413</b> or the bottom binding layer <b>414</b>. Similarly, the peaks of the downward facing cells are attached to the middle binding layer <b>413</b> or the top binding layer <b>412</b>. In some implementations, the middle binding layer <b>413</b> includes two sub-layers, one sub-layer associated with the top layer <b>411</b> and one sub-layer associated with the bottom layer <b>415</b>. The binding layers <b>412</b>, <b>413</b>, <b>414</b> link the void cells together forming the interdigitated cellular cushioning system <b>408</b>. In other implementations, the upward and downward facing cells are not protrusions of the binding layers <b>412</b>, <b>413</b>, <b>414</b>. Instead, the upward and downward facing cells are merely attached to the binding layers <b>412</b>, <b>413</b>, <b>414</b>.

0046<figref idref="DRAWINGS">FIG. 5</figref> illustrates a plan view of an example interdigitated cellular cushioning system <b>508</b>. The cushioning system <b>508</b> includes void cells (e.g., void cell <b>416</b>) arranged in a matrix bounded by the top binding layer <b>412</b> and a bottom binding layer (not shown). The cells alternate facing upwards and downward. In one implementation, each upward facing cell (e.g., cell <b>516</b>) is surrounded by downward facing cells and each downward facing cell (not shown) is surrounded by upward facing cells. The void cells are hollow chambers that resist deflection due to compressive forces, similar to compression springs. The force-deflection profile of the matrix of void cells is configurable based on the intended application of the cushioning system <b>508</b>.

0047Each upward facing cell is a protrusion of the top binding layer <b>512</b> and each downward facing cell is a protrusion of the bottom binding layer. Each peak of the upward facing cells is attached to the bottom binding layer. Similarly, each peak of the downward facing cells is attached to the top binding layer <b>512</b> (see e.g., at attachment point or area <b>526</b>). The binding layers link the void cells together forming the interdigitated cellular cushioning system <b>508</b>. In other implementations, the upward and downward facing cells are not protrusions of the top and bottom binding layers. Instead, the upward and downward facing cells are merely attached to the top and bottom binding layers.

0048In some implementations, the distances between the attachment points on a binding layer (e.g., binding layer <b>512</b>) and the centers of the open cells on the same binding layer are equidistant (i.e., distances A=B=C=D). This creates equal spacing between the void cells in the cushioning system <b>508</b>. This may apply to one or both of the binding layers. Further, this equal spacing provides a consistent force-deflection profile of the matrix of void cells across the surface area of the binding layers.

0049<figref idref="DRAWINGS">FIG. 6</figref> illustrates an elevation view of an example interdigitated cellular cushioning system <b>608</b> in an unloaded state. The cushioning system <b>608</b> includes void cells (e.g., void cell <b>610</b>) arranged in a matrix bounded by a top binding layer <b>612</b> and a bottom binding layer <b>614</b>. The cells alternate facing upwards and downward. Each peak of the upward facing cells is attached to the bottom binding layer <b>614</b>. Similarly, each peak (e.g., peak <b>618</b>) of the downward facing cells is attached to the top binding layer <b>612</b>. The binding layers <b>612</b>, <b>614</b> link the void cells together forming the interdigitated cellular cushioning system <b>608</b>.

0050The cushioning system <b>608</b> is placed in a test apparatus <b>628</b> that is configured to simulate a variety of loads that may be placed on the cushioning system <b>608</b>. The cushioning system <b>608</b> is not under load by the test apparatus <b>628</b>. As a result, the top binding layer <b>612</b> and bottom binding layer <b>614</b> may not be entirely flat and the void cells are not yet engaged to provide resistance to compression of the cushioning system <b>608</b>. Further, dimples (not shown) in the top binding layer <b>612</b> and/or bottom binding layer <b>614</b> may be present where void cells protruding from the opposite binding layer are attached to the top binding layer <b>612</b> and/or bottom binding layer <b>614</b> when the cushioning system <b>608</b> is not under load. The aforementioned features of the cushioning system <b>608</b> not under load may be intentionally designed into the cushioning system <b>608</b> or may be an artifact of the manufacturing process. Further, the magnitude of these features may vary.

0051<figref idref="DRAWINGS">FIG. 7</figref> illustrates an elevation view of an example interdigitated cellular cushioning system <b>708</b> loaded in a first load range. The cushioning system <b>708</b> includes void cells (e.g., void cell <b>710</b>) arranged in a matrix bounded by a top binding layer <b>712</b> and a bottom binding layer <b>714</b>. The cells alternate facing upwards and downward. Each peak of the upward facing cells is attached to the bottom binding layer <b>714</b>. Similarly, each peak (e.g., peak <b>718</b>) of the downward facing cells is attached to the top binding layer <b>712</b>. The binding layers <b>712</b>, <b>714</b> link the void cells together forming the interdigitated cellular cushioning system <b>708</b>.

0052The cushioning system <b>708</b> is placed in a test apparatus <b>728</b> that is configured to simulate a variety of loads that may be placed on the cushioning system <b>708</b>. A distributed load within the first load range (see <figref idref="DRAWINGS">FIG. 11</figref>, region <b>1</b>) is applied to the cushioning system <b>708</b> by the test apparatus <b>728</b> as illustrated by the opposed arrows. As a result, the top binding layer <b>712</b> and bottom binding layer <b>714</b> are flattened and any dimples are flattened. Further, the void cells are engaged and resisting the load within the first load range with relatively little deformation.

0053<figref idref="DRAWINGS">FIG. 8</figref> illustrates an elevation view of an example interdigitated cellular cushioning system <b>808</b> loaded in a second load range. The cushioning system <b>808</b> includes void cells (e.g., void cell <b>810</b>) arranged in a matrix bounded by a top binding layer <b>812</b> and a bottom binding layer <b>814</b>. The cells alternate facing upwards and downward. Each of the upward facing cells is attached to the bottom binding layer <b>814</b>. Similarly, each of the downward facing cells is attached to the top binding layer <b>812</b>. The binding layers <b>812</b>, <b>814</b> link the void cells together forming the interdigitated cellular cushioning system <b>808</b>.

0054The cushioning system <b>808</b> is placed in a test apparatus <b>828</b> that is configured to simulate a variety of loads that may be placed on the cushioning system <b>808</b>. A load within the second load range (see <figref idref="DRAWINGS">FIG. 11</figref>, region <b>2</b>) is applied to the cushioning system <b>808</b> by the test apparatus <b>828</b>. As a result, peaks (e.g., peak <b>718</b> of <figref idref="DRAWINGS">FIG. 7</figref>) of each of the void cells are flattened and the side walls of each of the void cells are reoriented vertically. In other implementations, the side walls are not reoriented vertically. However, the void cells are engaged and resisting the load within the second load range with flattening of the peaks of each of the void cells, but substantially no buckling of the side walls of each of the void cells. A consequence of the deformation of each of the void cells is that the top binding layer <b>812</b> and/or the bottom binding layer <b>814</b> may begin buckling as well.

0055<figref idref="DRAWINGS">FIG. 9</figref> illustrates an elevation view of an example interdigitated cellular cushioning system <b>908</b> loaded in a third load range. The cushioning system <b>908</b> includes void cells (e.g., void cell <b>910</b>) arranged in a matrix bounded by a top binding layer <b>912</b> and a bottom binding layer <b>914</b>. The cells alternate facing upwards and downward. Each of the upward facing cells is attached to the bottom binding layer <b>914</b>. Similarly, each of the downward facing cells is attached to the top binding layer <b>912</b>. The binding layers <b>912</b>, <b>914</b> link the void cells together forming the interdigitated cellular cushioning system <b>908</b>.

0056The cushioning system <b>908</b> is placed in a test apparatus <b>928</b> that is configured to simulate a variety of loads that may be placed on the cushioning system <b>908</b>. A load within the third load range (see <figref idref="DRAWINGS">FIG. 11</figref>, region <b>3</b>) is applied to the cushioning system <b>908</b> by the test apparatus <b>928</b>. As a result, the side walls of each of the void cells are substantially buckling as compared to the side walls of each of the void cells depicted in <figref idref="DRAWINGS">FIG. 8</figref>. Further, the void cells are spaced far enough apart that the buckling side walls do not touch one another. In other implementations, the void cells may be spaced closer together and press against one another under certain loading conditions. If the buckling side walls touch one another during compression, the force required per unit of deflection generally increases. A consequence of the deformation of each of the void cells is that the top binding layer <b>912</b> and/or the bottom binding layer <b>914</b> may be buckling as well.

0057<figref idref="DRAWINGS">FIG. 10</figref> illustrates an elevation view of an example interdigitated cellular cushioning system loaded in a fourth load range. The cushioning system <b>1008</b> includes void cells (no longer individually visible) arranged in a matrix bounded by a top binding layer <b>1012</b> and a bottom binding layer <b>1014</b>. The cells alternate facing upwards and downward. Each of the upward facing cells is attached to the bottom binding layer <b>1014</b>. Similarly, each of the downward facing cells is attached to the top binding layer <b>1012</b>. The binding layers <b>1012</b>, <b>1014</b> link the void cells together forming the interdigitated cellular cushioning system <b>1008</b>.

0058The cushioning system <b>1008</b> is placed in a test apparatus <b>1028</b> that is configured to simulate a variety of loads that may be placed on the cushioning system <b>1008</b>. A load within the fourth load range (see <figref idref="DRAWINGS">FIG. 11</figref>, region <b>4</b>) is applied to the cushioning system <b>1008</b> by the test apparatus <b>1028</b>. As a result, each of the void cells is fully compressed. Any further deformation of the cushioning system <b>1008</b> requires substantial increases in load. In one implementation, the fourth load range is referred to as densification.

0059<figref idref="DRAWINGS">FIG. 11</figref> illustrates a force over displacement graph <b>1100</b> with four load ranges (<b>1</b>, <b>2</b>, <b>3</b>, &amp; <b>4</b>), each with unique spring rate characteristics. A force applied substantially perpendicular to a top binding layer and a bottom binding layer of an interdigitated cellular cushioning system is plotted on the vertical axis of the graph <b>1100</b>. A displacement (or compressed distance) of the cushioning system is plotted on the horizontal axis of the graph <b>1100</b>. A spring rate refers to the ratio between the force (or load) applied to the cushioning system to the compressive displacement of the cushioning system. The force over displacement graph <b>1100</b> is merely one example of the presently disclosed technology. Various features of the cushioning systems discussed herein may be modified to yield a force over displacement graph <b>1100</b> with desired characteristics for a specific application.

0060In a first load region (illustrated by oval <b>1</b> on graph <b>1100</b>), relatively little force (i.e., 0 to 25 lbs.) is required to cause deformation of the cushioning system from 0 to 0.1 inches. This range is indicative of a load flattening the top binding layer and the bottom binding layer of the cushioning system and engaging all of the void cells in the cushioning system. For example, this load region is illustrated by <figref idref="DRAWINGS">FIG. 6</figref> (approximately 0 lbs. load, and 0 inches displacement) and <figref idref="DRAWINGS">FIG. 7</figref> (approximately 25 lbs. load and 0.1 inches displacement).

0061In a second load region (illustrated by oval <b>2</b> on graph <b>1100</b>), more force (i.e., 25 to 175 lbs.) per unit displacement is required to cause deformation of the cushioning system from 0.1 to 0.2 inches. This range is indicative of all of the void cells in the cushioning system being engaged and collapse of the peaks of each of the void cells. Further, the side walls of each of the void cells, which would normally taper inward slightly when uncollapsed begin to be deflected to an orientation generally perpendicular to the load. In other implementations, the side walls of each of the void cells are not necessarily substantially deflected, even under load. For example, this load region is illustrated by <figref idref="DRAWINGS">FIG. 8</figref>.

0062In a third load region (illustrated by oval <b>3</b> on graph <b>1100</b>), less force per unit displacement than region <b>2</b> but more force per unit displacement than region <b>1</b> (i.e., 175 to 300 lbs.) is required to cause deformation of the cushioning system from 0.2 to 0.35 inches. This range is indicative of the void cells buckling and collapsing in the cushioning system. For example, this load region is illustrated by <figref idref="DRAWINGS">FIG. 9</figref>.

0063In a fourth load region (illustrated by oval <b>4</b> on graph <b>1100</b>), an exponentially increasing force per unit displacement (i.e., 300 to 600 lbs.) is required to cause deformation of the cushioning system from 0.35 to 0.4 inches. This range is indicative of complete compression of the cushioning system and compression of the cushioning system materials themselves. In one implementation, the fourth load range is referred to as densification. For example, this load region is illustrated by <figref idref="DRAWINGS">FIG. 10</figref>.

0064One feature of the force over displacement graph <b>1100</b> is that the force required to compress the interdigitated cellular cushioning system increases throughout the range of compressed displacement. This is referred to herein as a monotonically increasing force-deflection curve. Further, an interdigitated cellular cushioning system with a monotonically increasing force-deflection curve provides monotonically collapsing void cells.

0065<figref idref="DRAWINGS">FIG. 12</figref> illustrates a first example force over time graph <b>1200</b> comparing impact performance of an interdigitated cellular cushioning system with impact performance of opposed void cellular cushioning systems. The graph <b>1200</b> illustrates an example impact applied substantially perpendicular to the binding layers of the various cushioning systems with a 2.355 kilogram (kg) mass moving at 5 meters per second (m/s). The force in Newtons (N) transmitted through the cushioning systems is illustrated on the vertical y-axis of the graph <b>1200</b> and the duration of time in milliseconds (ms) of the impact is illustrated on the horizontal x-axis of the graph <b>1200</b>. The example impact occurs within approximately 10.5 ms for each of the cushioning systems.

0066Solid line <b>1205</b> illustrates an example single-layer opposed void cushioning system utilizing a singular layer of opposed hemiellipsoidal voids, wherein each of the hemiellipsoidal voids are joined together at their peaks and the hemiellipsoidal voids are bound together by top and bottom binding layers. The example single-layer opposed void cushioning system is 0.75 inches (in) thick in this implementation. Solid line <b>1205</b> illustrates that the example single-layer opposed void cushioning system absorbs the least force of the illustrated example cushioning systems with a peak transmitted load of 12,724.73 N, which is concentrated between approximately 4.5 ms and 6 ms.

0067Dashed line <b>1210</b> illustrates an example double-layer opposed void cushioning system utilizing two layers of opposed hemiellipsoidal voids. Within each layer are hemiellipsoidal voids joined together at their peaks and bound together by top and bottom binding layers. The two layers are then stacked and joined together to form the double-layer opposed void cushioning system. The example double-layer opposed void cushioning system is 0.75 in thick in this implementation (i.e., each of the two layers is 0.375 in thick). Dashed line <b>1210</b> illustrates that the example double-layer opposed void cushioning system absorbs more force than the single-layer opposed void cushioning system with a peak transmitted load of 4,473.801 N, which is concentrated between approximately 3 ms and 6 ms.

0068Dotted line <b>1215</b> illustrates an example double-layer interdigitated void cushioning system utilizing two layers of interdigitated hemiellipsoidal voids. Each layer includes void cells arranged in a matrix bounded by a top binding layer and a bottom binding layer (See e.g., <figref idref="DRAWINGS">FIGS. 2, 3</figref>). The cells alternate facing upwards and downward. Each of the upward facing cells is attached to the bottom binding layer. Similarly, each of the downward facing cells is attached to the top binding layer. The binding layers link the void cells together forming a cushioning system layer. The two layers are then stacked and joined together to form the double-layer interdigitated void cushioning system (see e.g., <figref idref="DRAWINGS">FIG. 4</figref>). The example double-layer interdigitated void cushioning system is 0.75 in thick in this implementation (i.e., 0.375 in thick for each layer). Dotted line <b>1215</b> illustrates that the example double-layer interdigitated void cushioning system absorbs more force than both the single-layer opposed void cushioning system and the double-layer opposed void cushioning system with a peak transmitted load of 3,301.411 N, which is concentrated between approximately 3 ms and 6 ms.

0069In summary, the double-layer interdigitated void cushioning system illustrated by dotted line <b>1215</b> is particularly effective at absorbing kinetic energy and reducing the peak transmitted load caused by an impact. The double-layer interdigitated void cushioning system illustrated by dotted line <b>1215</b> is merely one example of the presently disclosed technology. Various features of the cushioning systems discussed herein may be modified to yield different force over time graphs with desired characteristics for different applications and expected loading conditions.

0070<figref idref="DRAWINGS">FIG. 13</figref> illustrates a second example force over time graph <b>1300</b> comparing impact performance of two interdigitated cellular cushioning systems with impact performance of an opposed void cellular cushioning system. The cushioning systems illustrated on graph <b>1300</b> are for a helmet application, although they could be used for other applications. The graph <b>1300</b> illustrates an example impact applied substantially perpendicular to the binding layers of the various cushioning systems with a 5.355 kg mass moving at 4.27 m/s. The force transmitted through the cushioning systems is illustrated on the vertical y-axis of the graph <b>1300</b> and the duration of time of the impact is illustrated on the horizontal x-axis of the graph <b>1300</b>. The example impact occurs within approximately 4.5 ms for each of the cushioning systems and each of the cushioning systems has a similar thickness (e.g., 0.5-1.0 in).

0071Line <b>1305</b> illustrates an example helmet without a cushioning system. The example helmet without a cushioning system transmits the greatest amount of force with a peak transmitted load of 32,000.29 N, which is concentrated between approximately 0 ms and 1.75 ms.

0072Line <b>1310</b> illustrates an example single-layer opposed void helmet cushioning system utilizing a singular layer of opposed hemiellipsoidal voids, wherein each of the hemiellipsoidal voids are joined together at their peaks and the hemiellipsoidal voids are bound together by top and bottom binding layers. Line <b>1310</b> illustrates that the example single-layer opposed void helmet cushioning system absorbs significantly more force than the example helmet without a cushioning system with a peak transmitted load of 22,070.06 N, which is concentrated between approximately 0 ms and 2.5 ms.

0073Line <b>1315</b> illustrates an example single-layer interdigitated void helmet cushioning system utilizing void cells arranged in a matrix bounded by a top binding layer and a bottom binding layer (See e.g., <figref idref="DRAWINGS">FIGS. 2, 3</figref>). The cells alternate facing upwards and downward. Each of the upward facing cells is attached to the bottom binding layer. Similarly, each of the downward facing cells is attached to the top binding layer. The binding layers link the void cells together forming the single-layer interdigitated void helmet cushioning system. Line <b>1315</b> illustrates that the example single-layer interdigitated void helmet cushioning system absorbs a similar amount of force as the single-layer opposed void helmet cushioning system with a peak transmitted load of 22205.24 N, which is concentrated between approximately 0 ms and 2.5 ms.

0074Line <b>1320</b> illustrates an example double-layer interdigitated void helmet cushioning system utilizing two layers of interdigitated hemiellipsoidal voids. Each layer includes void cells arranged in a matrix bounded by a top binding layer and a bottom binding layer (see e.g., <figref idref="DRAWINGS">FIGS. 2, 3</figref>). The cells alternate facing upwards and downward. Each of the upward facing cells is attached to the bottom binding layer. Similarly, each of the downward facing cells is attached to the top binding layer. The binding layers link the void cells together forming a cushioning system layer. The two layers are then stacked and joined together to form the double-layer interdigitated void helmet cushioning system (see e.g., <figref idref="DRAWINGS">FIG. 4</figref>). Line <b>1320</b> illustrates that the example double-layer interdigitated void helmet cushioning system absorbs more force than both the single-layer opposed void helmet cushioning system illustrated by line <b>1310</b> and the single-layer interdigitated void helmet cushioning system illustrated by line <b>1315</b>. The example double-layer interdigitated void helmet cushioning system has a peak transmitted load of 11.240.39 N, which is concentrated between approximately 0 ms and 3 ms.

0075In summary, the double-layer interdigitated helmet void cushioning system illustrated by line <b>1320</b> is particularly effective at absorbing kinetic energy and reducing the peak transmitted load caused by an impact. In helmet applications, this can reduce the occurrence of concussion injuries to individuals wearing so-equipped helmets. The double-layer interdigitated helmet void cushioning system illustrated by line <b>1320</b> is merely one example of the presently disclosed technology. Various features of the cushioning systems discussed herein may be modified to yield different force over time graphs with desired characteristics for different applications and expected loading conditions.

0076<figref idref="DRAWINGS">FIG. 14</figref> illustrates a third example force over time graph <b>1400</b> comparing impact performance of an interdigitated cellular cushioning system with impact performance of an opposed void cellular cushioning system. The graph <b>1400</b> illustrates an example impact applied substantially perpendicular to the binding layers of the cushioning systems with a 2.355 kg mass moving at 7.0 m/s. The force transmitted through the cushioning systems is illustrated on the vertical y-axis of the graph <b>1400</b> and the duration of time of the impact is illustrated on the horizontal x-axis of the graph <b>1400</b>. The example impact occurs between approximately 0.5 ms and 3.0 ms for each of the cushioning systems.

0077Line <b>1405</b> illustrates an example opposed void cushioning system utilizing a singular layer of opposed hemiellipsoidal voids, wherein each of the hemiellipsoidal voids are joined together at their peaks and the hemiellipsoidal voids are bound together by top and bottom binding layers. The opposed void cushioning system is approximately 0.75 in thick. Line <b>1405</b> illustrates that the example opposed void cushioning system has a peak transmitted load of 25,553.44 N, which is concentrated between approximately 1.75 ms and 3.0 ms.

0078Line <b>1410</b> illustrates an example interdigitated void cushioning system utilizing a singular layer of void cells arranged in a matrix bounded by a top binding layer and a bottom binding layer (see e.g., <figref idref="DRAWINGS">FIGS. 2, 3</figref>). The cells alternate facing upwards and downward. Each of the upward facing cells is attached to the bottom binding layer. Similarly, each of the downward facing cells is attached to the top binding layer. The binding layers link the void cells together forming the interdigitated void cushioning system. The interdigitated void cushioning system is approximately 0.325 in thick. Line <b>1410</b> illustrates that the example interdigitated void cushioning system transmits approximately 6% more force than the opposed void cushioning system with a peak transmitted load of 27,175.55 N, which is concentrated between approximately 1.75 ms and 3.0 ms.

0079In summary, the interdigitated void cushioning system illustrated by line <b>1410</b> is only approximately 6% less effective than the opposed void cushioning system at absorbing impact force while utilizing approximately 50% of the overall material thickness of the opposed void cushioning system. This makes the interdigitated void cushioning system particularly effective in space-limited areas. The interdigitated void cushioning system illustrated by line <b>1410</b> is merely one example of the presently disclosed technology. Various features of the cushioning systems discussed herein may be modified to yield a different force over time graphs with desired characteristics for different applications and expected loading conditions.

0080<figref idref="DRAWINGS">FIG. 15A</figref> illustrates an example uncompressed cell <b>1510</b> in an interdigitated cellular cushioning system <b>1500</b>. The cell <b>1510</b> is uncompressed and has four distinct regions. Region A is occupied by a dimple in a top binding layer <b>1512</b>. The dimple may be designed as a part of the cushioning system <b>1500</b> or an artifact of the manufacturing process used to create the cushioning system <b>1500</b>. Region B is occupied by the domed or peak portion of the cell <b>1510</b>. Region C is occupied by the side-walls of the cell <b>1510</b> and Region D is occupied by the base of the cell <b>1510</b>. In one implementation, <figref idref="DRAWINGS">FIG. 15A</figref> corresponds to <figref idref="DRAWINGS">FIG. 6</figref> and <figref idref="DRAWINGS">FIG. 11</figref> at 0 lbs of load and 0 in of displacement.

0081<figref idref="DRAWINGS">FIG. 15B</figref> illustrates an example cell <b>1510</b> in an interdigitated cellular cushioning system <b>1500</b> compressed in a first load range. Compression of the cell <b>1510</b> removes the dimple and region A, which was occupied by the dimple in <figref idref="DRAWINGS">FIG. 15A</figref>. The cell <b>1510</b> is under load but has not substantially deflected from its shape in <figref idref="DRAWINGS">FIG. 15A</figref>. As a result, regions B, C, and D are relatively unchanged with respect to <figref idref="DRAWINGS">FIG. 15A</figref>. In one implementation, <figref idref="DRAWINGS">FIG. 15B</figref> corresponds to <figref idref="DRAWINGS">FIG. 7</figref> and <figref idref="DRAWINGS">FIG. 11</figref>, load region <b>1</b>.

0082<figref idref="DRAWINGS">FIG. 15C</figref> illustrates an example cell <b>1510</b> in an interdigitated cellular cushioning system <b>1500</b> compressed in a second load range. Further compression of the cell <b>1510</b> changes the shape of the cell <b>1510</b>. The domed or peak portion of the cell <b>1510</b> illustrated in <figref idref="DRAWINGS">FIGS. 15A and 15B</figref> is mostly, if not completely, collapsed. Thus, region B is reduced to nearly zero vertical dimension. Further, the base of the cell <b>1510</b> is compressed and also reduced in size. Region C grows to encompass most of the height of the cell <b>1510</b> as compared to <figref idref="DRAWINGS">FIGS. 15A and 15B</figref>. In one implementation, <figref idref="DRAWINGS">FIG. 15C</figref> corresponds to <figref idref="DRAWINGS">FIG. 8</figref> and <figref idref="DRAWINGS">FIG. 11</figref>, load region <b>2</b>.

0083<figref idref="DRAWINGS">FIG. 15D</figref> illustrates an example cell <b>1510</b> in an interdigitated cellular cushioning system <b>1500</b> compressed in a third load range. Further compression of the cell <b>1510</b> buckles the side-walls of the cell <b>1510</b>. The cell <b>1510</b> collapses as the side-walls of the cell <b>1510</b> collapse further. In one implementation, <figref idref="DRAWINGS">FIG. 15D</figref> corresponds to <figref idref="DRAWINGS">FIG. 9</figref> and <figref idref="DRAWINGS">FIG. 11</figref>, load region <b>3</b>.

0084<figref idref="DRAWINGS">FIG. 15E</figref> illustrates an example cell <b>1510</b> in an interdigitated cellular cushioning system <b>1500</b> compressed in a fourth load range. Further compression of the cell <b>1510</b> fully buckles the side-walls and fully collapses of the cell <b>1510</b>. Any further compression of the cell <b>1510</b> is due to compression of the material used to construct the cell (referred to as densification herein). In one implementation, <figref idref="DRAWINGS">FIG. 15E</figref> corresponds to <figref idref="DRAWINGS">FIG. 10</figref> and <figref idref="DRAWINGS">FIG. 11</figref>, load region <b>4</b>.

0085<figref idref="DRAWINGS">FIG. 16</figref> illustrates example operations <b>1600</b> for using an interdigitated cellular cushioning system. A first collapsing operation <b>1605</b> collapses a first matrix of void cells interconnected by a bottom binding layer. The first collapsing operation <b>1605</b> may occur as a result of an impact or explosion adjacent the bottom binding layer that applies substantial kinetic energy to the bottom binding layer. The collapse of the first matrix of void cell absorbs some of the kinetic energy applied to the bottom binding layer. A second collapsing operation <b>1610</b> collapses a second matrix of void cells interdigitated with the first matrix of void cells and interconnected by a lower-middle binding layer. The collapse of the second matrix of void cell absorbs more of the kinetic energy caused by the impact or explosion, for example.

0086A third collapsing operation <b>1615</b> collapses a third matrix of void cells interconnected by an upper-middle binding layer. The third collapsing operation <b>1615</b> may occur as a result of energy from the impact or explosion traveling through the collapsed first and second matrices of void cells to the third matrix of void cells. The collapse of the third matrix of void cell absorbs more of the kinetic energy caused by the impact or explosion, for example. A fourth collapsing operation <b>1620</b> collapses a fourth matrix of void cells interdigitated with the third matrix of void cells and interconnected with a top binding layer without collapsing the top binding layer. The first, second, third, and fourth matrices of void cells and the bottom, lower-middle, upper-middle, and top binding layers in combination form the interdigitated cellular cushioning system. The collapse of the fourth matrix of void cell absorbs more of the kinetic energy caused by the impact or explosion, for example.

0087If sufficient energy is absorbed by the collapse of the first, second, third, and fourth matrices of void cells, the top binding layer is not collapsed. This protects personnel and/or equipment adjacent the top binding layer. In other implementations, the top binding layer is partially collapsed, but less so than the bottom, lower-middle, and upper-middle binding layers, partially protecting the personnel and/or equipment adjacent the top binding layer. In some implementations, only two (rather than four) matrices of void cells are used to form the interdigitated cellular cushioning system. In other implementations, greater than four matrices of void cells are used to form the interdigitated cellular cushioning system.

0088For example, the interdigitated cellular cushioning system may absorb an explosion that deflects a layer of armor on one side of the interdigitated cellular cushioning system without deflecting a flooring layer on the opposite side of the interdigitated cellular cushioning system. The cellular cushioning system may act to absorb energy of the explosion so that the flooring does not transfer the energy to users standing on the floor.

0089<figref idref="DRAWINGS">FIG. 17</figref> illustrates an example thermoforming manufacturing process <b>1700</b> for making a 2-layer interdigitated cellular cushioning system <b>1743</b>. Two rolls of thermoplastic sheet stock <b>1730</b>, <b>1731</b> are fed from rolls <b>1732</b>, <b>1733</b> over rollers <b>1734</b> to sheet stock heaters <b>1735</b> to raise the temperature of the sheet stock to substantially its normal forming temperature. The sheet stock <b>1730</b>, <b>1731</b> is then advanced to a form station <b>1736</b> with an upper mold <b>1737</b> and a lower mold <b>1738</b>. Vacuum is applied to the molds <b>1737</b>, <b>1738</b> to force the upper sheet material <b>1731</b> into the upper mold <b>1737</b> and the lower sheet material <b>1730</b> into the lower mold <b>1738</b>. Air pressure may also be applied between the sheets to assist in forcing the thermoplastic sheet stock <b>1730</b>, <b>1731</b> firmly into the molds <b>1737</b>, <b>1738</b>. Formed sheets <b>1739</b>, <b>1740</b> of thermoplastic with hemiellipsoidal protrusions are removed from the molds <b>1737</b>, <b>1738</b> and joined together by orienting the hemiellipsoidal protrusions between one another and welding the peaks of each of the hemiellipsoidal protrusions to the opposite sheet of thermoplastic material. The resulting material is a first layer of interdigitated cellular cushioning <b>1741</b>.

0090A second layer of interdigitated cellular cushioning <b>1742</b> is manufactured in a similar process as discussed above with regard to the first layer of interdigitated cellular cushioning <b>1741</b>. In some implementations, the formed sheets are merely placed in the aforementioned position without welding. The formed sheets are held in place by the additional welds discussed below. However, in this implementation, only the hemiellipsoidal protrusions of the first layer of interdigitated cellular cushioning that meet the second layer of interdigitated cellular cushioning, and vice versa, are welded.

0091The second layer of interdigitated cellular cushioning <b>1742</b> may be manufactured simultaneously using additional equipment as depicted in <figref idref="DRAWINGS">FIG. 17</figref> or manufactured sequentially after the first layer of interdigitated cellular cushioning <b>1741</b> using the same equipment as the first layer of interdigitated cellular cushioning <b>1741</b>. Further, one mold may be used to sequentially manufacture the formed sheets <b>1739</b>, <b>1740</b> of thermoplastic rather than the depicted two molds <b>1737</b>, <b>1738</b> manufacturing the formed sheets <b>1739</b>, <b>1740</b> simultaneously. In another implementation, separate sheets of thermoplastic may be used instead of the depicted continuous rolls of thermoplastic sheet stock. The sheets move from station to station (e.g., from heating to molding) in such a process.

0092The first layer of interdigitated cellular cushioning <b>1741</b> and the second layer of interdigitated cellular cushioning <b>1742</b> are placed adjacent one another with peaks of hemiellipsoidal protrusions on each of the cellular cushioning layers <b>1741</b>, <b>1742</b> aligned. The cellular cushioning layers <b>1741</b>, <b>1742</b> are joined by welding at peaks of the hemiellipsoidal protrusions where the four layers of thermoplastic material meet. The resulting material is the 2-layer interdigitated cellular cushioning system <b>1743</b>. In some implementations, additional layers of interdigitated cellular cushioning or other materials may be applied to the interdigitated cellular cushioning system <b>1743</b> to give the system <b>1743</b> different features.

0093As described, each of the cellular cushioning layers <b>1741</b>, <b>1742</b> and/or formed sheets <b>1739</b>, <b>1740</b> of thermoplastic with hemiellipsoidal protrusions can be constructed of different thermoplastic materials. Accordingly, the features of the interdigitated cellular cushioning system <b>1743</b> may be tuned for specific applications. For example, the layer <b>1741</b> may be composed of a thicker, heavier thermoplastic material, while the layer <b>1742</b> may be composed of a thinner, lighter thermoplastic material. Similarly, the sheet <b>1739</b> may be composed of a thicker, heavier thermoplastic material, while the sheet <b>1740</b> may be composed of a thinner, lighter thermoplastic material. Having corresponding cellular cushioning layers <b>1741</b>, <b>1742</b> and/or formed sheets <b>1739</b>, <b>1740</b> of different materials increases the ability of the designer to construct differing degrees of flexibility or resistance into specific areas of the system <b>1743</b>. By varying the materials employed in terms of specific properties such as tensile strength, material thickness, and elongation and by varying the hemiellipsoidal protrusion dimensions, a number of consistently reproducible regions of desired resistance and flexibility can be engineered into the system <b>1743</b> to meet specific requirements.

0094<figref idref="DRAWINGS">FIG. 18</figref> illustrates example operations <b>1800</b> for manufacturing an interdigitated cellular cushioning system. A heating operation <b>1805</b> heats thermoplastic sheet stock to a forming temperature. The thermoplastic sheet stock may be a continuation roll or discrete sheets of material. A molding operation <b>1810</b> molds the sheet stock into a first sheet with void cell protrusions and a second sheet with void cell protrusions. The molding operation <b>1810</b> may utilize one mold to form the first sheet and the second sheet sequentially or two molds to form the first sheet and the second sheet simultaneously. The void cell protrusions may have a variety of shapes (e.g., hemiellipsoidal), sizes, and spacings. Further, the molding operation <b>1810</b> may utilize one or both of positive and negative pressures to aid the sheets in conforming to the mold(s).

0095An arranging operation <b>1815</b> arranges the first molded sheet adjacent the second molded sheet with the void cells oriented between one another, protruding toward and contacting the opposite molded sheet (referred to herein as interdigitation). A welding operation <b>1820</b> welds peaks of each of the void cells to the opposite molded sheet to form a first layer of interdigitated cellular cushioning. In one implementation, the welding operation <b>1820</b> is accomplished by bringing a hot iron from above and a corresponding hot iron or other structure from below and providing sufficient thermal energy and pressure from the hot iron(s) to melt and coalesce the molded sheets together at the point of the contact with the hot iron(s). In some implementations, the welding operation <b>1820</b> is optional as welding operation <b>1835</b> alone may sufficiently join the molded sheets together.

0096A forming operation <b>1825</b> forms a second layer of interdigitated cellular cushioning. The forming operation <b>1825</b> may be accomplished by repeating operations <b>1805</b>-<b>1820</b>, for example. An arranging operation <b>1830</b> arranges the first cushioning layer adjacent the second cushioning layer with peaks of the void cells on each of the first and second cushioning layers aligned with one another. As a result, the four sheets of thermoplastic material are adjacent one another at the peaks of the outwardly facing void cells. The welding operation <b>1835</b> welds peaks of the void cells where the four sheets of thermoplastic material meet. The welding operation <b>1835</b> may be accomplished as discussed above with regard to the welding operation <b>1820</b>. As a result, the four sheets of thermoplastic material are melted and coalesced together at the weld points and the resulting structure is a 2-layer interdigitated cellular cushioning system. In some implementations, additional layers of interdigitated cellular cushioning or other materials may be added to the interdigitated cellular cushioning system to achieve desired properties of the interdigitated cellular cushioning system. In some implementations, the additional layers may include a floor for users to stand upon and/or armor to protect users from impact by various projectiles.

0097The above specification, examples, and data provide a complete description of the structure and use of exemplary embodiments of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. Furthermore, structural features of the different embodiments may be combined in yet another embodiment without departing from the recited claims.